The objectives of the proposed research are: (a) Identify more precisely the bacterial ligands involved in the adherence of the organisms to membrane receptors on the surfaces of host cells, especially epithelial cells and phagocytic cells, (b) To isolate and identify the membrane receptors which serve to attach bacteria to host cells. Special emphasis will be focused on studying the specificity and affinity of the binding of the purified ligand to its receptor or receptor analogues. Initially our studies will be limited to streptococci and Escherichia coli. We have already demonstrated that one of the bacterial ligands of group A streptococci is lipoteichoic acid and that the membrane receptor for attachment of Escherichia coli to host cells bears mannose residues. It is hoped that the studies on bacterial adherence will shed light upon the mechanisms by which bacteria colonize mucosal surfaces to initiate the infectious process. A better understanding of these mechanisms and the identification of the specific ligands and receptors involved in the interaction may lead to the development of methods for intervening in the infectious process before the bacteria gains a foothold on mucosal surfaces and thereby cause tissue injure.